I have a few accounts at Scottrade, have been using them for months, and have never encountered technical difficulties during the trading day. And they consistently receive high customer satisfaction ratings in surveys.

The Fidelity website tells me that's you'd have to make 120 trades per year to qualify for $8 trades. If you're making this many annual trades, your investing behavior is going to cost you far more in the long run than any glitches at Scottrade.